1. Field of the Invention
The present invention relates to a motor drive controller and a control method of motor drive controller.
2. Description of the Related Art
Recently, since a brushless motor has a long life span and is maintenance-free, the brushless motor has been widely used. In stationary equipment, since there is a margin in an installment space, a brushless motor and a control circuit are often separately configured. However, in portable equipment, since the margin in an installment space is small, a brushless motor and a control circuit are often configured as a unified body. The control circuit in the related art is specially configured to drive a specific type of brushless motor.
By improving a degree of freedom in selecting a type of a brushless motor, it is possible to decrease a procurement cost and to improve performance. Accordingly, the control circuit is preferred to have a capability to drive an arbitrary type of brushless motor as well as a specific type of brushless motor.
In JP-A-2004-072903, it is described that “An object is to provide a brushless motor which has low noise and low vibration and is easily replaceable without changing a rotation speed detection circuit that is provided in equipment to which the brushless motor is installed, by outputting a rotation speed signal of the same number of pulses as a motor with eight rotor poles even when the number of rotor poles is ten,” and the means of solving thereof describes that “A rotation speed pulse signal of four pulses or twelve pulses per rotation can be output even when the number of rotor poles is ten, by installing a rotation speed pulse signal frequency converting circuit 17.” Accordingly, brushless motors having different numbers of rotor poles can be commonly used in the same equipment (system).
In paragraph [0027] of JP-A-2004-072903, it is described that “The output signals 15ao to 15co of the position detecting elements 15a to 15c are signals of five pulses per rotation in which electrical angles are different by 120 degrees. The position detection signal processing circuit 16 processes the output signals 15ao to 15co and outputs a signal 15ao of five pulses per rotation or a signal 15bo of fifteen pulses per rotation. The rotation speed pulse signal frequency converting circuit 17 frequency-converts the signal 15ao or the signal 15bo and outputs a signal 17ao of four pulses per rotation or a signal 17bo of twelve pulses per rotation. The signal 17ao or the signal 17bo is output to the outside through the rotation speed pulse signal output circuit 18.” That is, the frequency of the rotation speed pulse signal is converted by the rotation speed pulse signal frequency converting circuit.
However, the technique described in JP-A-2004-072903 is based on the premise that a motor outputs plural rotation speed pulse signals (hereinafter, referred to as “rotation pulse signal”) in which electrical angles thereof are different by a predetermined angle. Accordingly, the technique cannot be applied to a system based on the premise that a motor outputs a single rotation pulse signal. Specifically, the technique described in JP-A-2004-072903 may not be applied when a motor outputting two pulses per rotation is used in a system based on the premise that a motor outputs a single rotation pulse signal and four pulses per rotation. That is, when a single rotation pulse signal is used, the single rotation pulse signal cannot be converted in frequency and thus there is a problem in that the motor itself should be changed or the frequency should be multiplied by two by a microcomputer.
A rotation pulse signal FG slowly increases in frequency until a motor reaches a target rotation speed after the motor is started, and decreases in period in inverse proportion thereto. When it is intended to measure the period of the rotation pulse signal FG using a microcomputer, a scaler of a timer should be scanned to cope with the change in frequency, the processing is complicated, and thus a high-speed microcomputer is required. When it is intended to output a signal obtained by multiplying the measured period, a timer other than the timer used to measure the period of the rotation pulse signal FG is required and thus a high-performance microcomputer having two or more timers is required. Accordingly, there is a problem in that the system cost is high.